linux-kernel - [PATCH v3 2/3] scsi: 3w-9xxx: Reduce scope of structure packing

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Date:   Sat,  8 Aug 2020 19:47:26 -0500
From:   Samuel Holland <samuel@...lland.org>
To:     Adam Radford <aradford@...il.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Arnd Bergmann <arnd@...db.de>
Cc:     linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        Samuel Holland <samuel@...lland.org>
Subject: [PATCH v3 2/3] scsi: 3w-9xxx: Reduce scope of structure packing

Currently, all command packet structs used by this driver are packed.
However, only one (TW_SG_Entry) actually needs to be packed, because it
uses 64-bit addresses at 32-bit alignment. To improve the quality of
generated code, stop packing all of the other command packet structs.
This requires adjusting the type of one misaligned "reserved" member.

After this change, pahole reports that only one type had its layout
change: the tw_compat_info member of TW_Device_Extension is now
naturally aligned.

Signed-off-by: Samuel Holland <samuel@...lland.org>
---
 drivers/scsi/3w-9xxx.h | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/drivers/scsi/3w-9xxx.h b/drivers/scsi/3w-9xxx.h
index e65dafda2e3e..36b865eca67d 100644
--- a/drivers/scsi/3w-9xxx.h
+++ b/drivers/scsi/3w-9xxx.h
@@ -471,13 +471,17 @@ printk(KERN_WARNING "3w-9xxx: ERROR: (0x%02X:0x%04X): %s.\n",a,b,c); \
 #define TW_PADDING_LENGTH (sizeof(dma_addr_t) > 4 ? 8 : 0)
 #define TW_CPU_TO_SGL(x) (sizeof(dma_addr_t) > 4 ? cpu_to_le64(x) : cpu_to_le32(x))
 
-#pragma pack(1)
+#if IS_ENABLED(CONFIG_ARCH_DMA_ADDR_T_64BIT)
+typedef u64 twa_addr_t;
+#else
+typedef u32 twa_addr_t;
+#endif
 
 /* Scatter Gather List Entry */
 typedef struct TAG_TW_SG_Entry {
-	dma_addr_t address;
+	twa_addr_t address;
 	u32 length;
-} TW_SG_Entry;
+} __packed TW_SG_Entry;
 
 /* Command Packet */
 typedef struct TW_Command {
@@ -496,12 +500,12 @@ typedef struct TW_Command {
 		struct {
 			u32 lba;
 			TW_SG_Entry sgl[TW_ESCALADE_MAX_SGL_LENGTH];
-			dma_addr_t padding;
+			twa_addr_t padding;
 		} io;
 		struct {
 			TW_SG_Entry sgl[TW_ESCALADE_MAX_SGL_LENGTH];
 			u32 padding;
-			dma_addr_t padding2;
+			twa_addr_t padding2;
 		} param;
 	} byte8_offset;
 } TW_Command;
@@ -531,7 +535,7 @@ typedef struct TAG_TW_Command_Apache_Header {
 	unsigned char err_specific_desc[98];
 	struct {
 		unsigned char size_header;
-		unsigned short reserved;
+		unsigned char reserved[2];
 		unsigned char size_sense;
 	} header_desc;
 } TW_Command_Apache_Header;
@@ -631,8 +635,6 @@ typedef struct TAG_TW_Compatibility_Info
 	unsigned short fw_on_ctlr_build;
 } TW_Compatibility_Info;
 
-#pragma pack()
-
 typedef struct TAG_TW_Device_Extension {
 	u32                     __iomem *base_addr;
 	unsigned long	       	*generic_buffer_virt[TW_Q_LENGTH];
-- 
2.26.2